Impacts Of Stokes Drift On Summer Ocean Dynamics In Bohai Sea

Among the physical processes of turbulent mixing,wave mixing is an important research direction of ocean mixing.The upper ocean structure can be affected by waves,and the Stokes drift is the main way to affect the turbulent mixing of the upper ocean.The Stokes drift modifies the upper ocean turbulence through large scale CoriolisStokes force,small scale Langmuir turbulence and resolved-scale Craik-Leibovich vortex force.A one-way coupled POM-SWAN model is applied to study the impacts of Stokes drift on summer ocean dynamics in Bohai Sea.Both Coriolis-Stokes force and resolvedscale Craik-Leibovich vortex force are included in the horizontal momentum equation.The turbulence closure model is modified to contain the parameterization of Langmuir turbulence.Numerical results show that the improved model reproduces the sea surface temperature better than the original one.Stokes drift considerably contributes to temperature variability at different vertical levels,with the maximum temperature change of about 0.4℃.Based on the diagnostic experiments,the impacts of CoriolisStokes force and resolved-scale Craik-Leibovich vortex force on temperature are much weaker than that of Langmuir turbulence.The horizontal distribution of Langmuir number indicates that the Langmuir turbulence is prevalent in Bohai Sea.The large vertical kinematic viscosity coefficient,containing the Langmuir turbulence,would lead to a strong vertical mixing.In addition,the Stokes drift affects the current as well.It reduces the current velocity and makes the current vertically uniform.The impacts of Stokes drift under typhoon are also explored in this paper.When the typhoon enters Bohai Sea,Stokes drift makes contributions to turbulent mixing,the sea surface temperature and current decrease rapidly,and the mixed layer deepening.When the typhoon reaches the Central Sea Area,the continuous action of Stokes drift transfers more heat from the upper layer to a deeper layer,the phenomenon of sea surface temperature cooling is obvious,and the thermal stratification is destroyed.The vertical kinematic viscosity coefficient is controlled by the wind speed and the angle between the wind direction and Stokes drift direction.During the post typhoon stage,the responses of temperature and current to Stokes drift are lagged,they variety slowly in the mixed layer.